Open surgical intervention was once the standard treatment for the removal of calculi or stones, especially when such calculi are deposited in a body lumen other than the bladder. But other less invasive techniques have emerged as safe and effective alternatives. Lithotripsy, the crushing of stones that develops in the body into fragments that are easier to remove, is one such technique. Lithotripsy devices have been developed which utilize electrohydraulic probes, ultrasonic probes, electromechanical impactors, or a pin driven by compressed air. These devices typically use percutaneous endoscopic techniques and are configured to be introduced into the body through small puncture sites to avoid open surgical intervention. Focused shock waves can also be delivered from an external source in a non-invasive procedure known as extracorporeal shock wave lithotripsy (ESWL).
Recently, lasers have been used as an alternative source of energy in lithotripsy, especially for the destruction of renal and bilary stones. Lasers are suited for minimally invasive lithotripsy because the diameter of the laser fiber is small and the aperture of the working channel can be minimized. An extensive review of the use of lasers for lithotripsy is provided in the book entitled “Laser Lithotripsy,” edited by R. Stein, Springer Verlag, 1988. A fiber optic that travels along the longitudinal axis of a rigid or flexible endoscope typically transmits the laser beam. Various types of laser lithotripsy systems with a variety of laser sources, including pulsed dye laser, alexandrite laser, neodymium laser and holmium laser, have been developed.
A common problem in intracorporeal lithotripsy treatment is the difficulty in restricting target movement. For example, when using pulsed lasers such as the holmium yttrium-aluminum-garnet (Ho:YAG) laser, higher frequency pulsation and higher energy in each pulse produce quicker fragmentation of the stone, but also produce significant stone mobility, which decreases treatment efficiency. Lower frequency to pulsation and lower pulse energy may result in less significant stone mobility, but the treatment time will be prolonged. Regardless of energy level of each emission, stones of smaller sizes present an inherent mobility problem. Incomplete lithotripsy treatment of smaller stones or debris can leave a nidus for future stone growth.
Another problem often encountered by a lithotripsy endoscopist involves the suction tube that is found in some endoscopes. Such a conduit is generally connected to a pump that produces a vacuum when in operation and clogging at distal ends by stones and their fragments has been widely reported. See. e.g. U.S. Pat. No. 4,146,019 to Bass et al. Severe clogging may necessitate repeated removal, cleaning and reinsertion of the endoscope during an operation.